[mojo]

On the not-working XP box, right-click on my computer, then go to manage. Go to local users and groups. Under the Administrators group (and possibly others), make sure that the appropriate domain groups/users are included. I can't tell you precisely what will be appropriate, though it's fairly appropriate for the Domain Admins to be included in the Administrators group. You may just have to copy the configuration from the other XP box that seems to be working fine.